ProjectSummary: The recent finding that early introduction of peanut can prevent ~70-90% of peanut allergy is a major step towards prevention of food allergy. However, because that finding was from a clinical trial in a very select population, there are several major questions that must be answered in order to implement these findings into clinical practice without causing more harm than good. These questions include who, if anyone, should be screened prior to early introduction for peanut allergy, how this screening should be done, and what quantity of peanut ingestion is needed to prevent peanut allergy. Our goal is to answer these critical questions so that the potential of these recent findings can be realized. To that end, we will enroll 400 infants at high- risk of peanut allergy. These infants will be given a peanut skin prick test, peanut food challenge and have blood drawn for measurement of peanut IgE, and then will be followed for assessment of peanut consumption and development of peanut allergy. Aim 1 is to determine the rate of peanut reactivity in infancy among these high risk groups, Aim 2 is to characterize the performance of possible screening tests for peanut allergy in infancy, and Aim 3 is to characterize the peanut consumption patterns of these infants after screening and to determine the association with development of peanut allergy. Exploratory Aim 4 is to understand racial/ethnic disparities in risk of reactivity and diagnostic parameters of screening tests.